If this is the control number on your W-2 and the TurboTax program is giving you an error message, leave that box blank.
The Control number is given and used by your payroll department.
It has no tax relevance and is not used by tax software.
If this control number is stopping you from being able to import your W-2, you will need to type it in.
If this control number is for something else, please continue your question.